Method and apparatus for generating a superficial structure

ABSTRACT

A method and related apparatus for producing an embossing on a substrate using a digital printing technology includes the application of an embossing liquid, for example a water-based liquid, on a non-polymerized resin layer and the subsequent polymerization of the resin with UV curing.

FIELD OF THE INVENTION

The present invention relates to a method and apparatus for generating asuperficial structure.

In particular, the invention relates to a method for producing anembossed three dimensional coating on a substrate by means of digitalprinting.

The present invention belongs to the technical field of materials andmethods for generating three dimensionality and embossings on surfacesof articles, substrates, supports in different types of material, suchas, for example, panels for the production of floors, coatings,furnishings and more generally for architectural and design surfaces.The technology object of the invention may be further used to reproducemicrostructures usable in the fields of biology, optics and electronics.

BACKGROUND ART

Digital printing, and in particular inkjet printing, is increasinglyestablishing itself in industrial sectors, replacing traditional methodsbased on analog printing. The advantages of digital printing areremarkable and comprise high flexibility, the possibility to producelimited runs and the reduction of waste of consumables.

In particular, the reproduction of wood on various materials is atypical application of digital printing in the production of floors,furniture panels, skirting boards, profiles and in general in the fieldof design and architecture.

Typically, materials may consist of wood and derived products(MDF/HDF/particleboard/plywood), plastics (PVC/polyolefin), metals, onwhich the image is printed, which, in turn, is usually protected by apaint so as to increase the abrasion and scratch resistance thereof.

In particular, in the case of floors and furniture panels, the finishingafter printing involves the use of a melamine resin layer (laminates) orof a paint applied by means of usual techniques (roller/spray/thinlayer/die). The paint may be of various nature, photocurable, epoxy,polyurethane, hot-melt.

When reproducing natural materials, such as wood and stones, beside theimage it is necessary to reproduce the superficial structure thereof, inorder to obtain a material more similar to the original one also in thetouch.

Embossing is usually performed on the superficial layer and may beobtained by various methods, traditionally by means of pressing withmolds, rollers or belts on which the structure to be impressed isreproduced. The process may take place by pressing on not completelyhardened resins, on thermoplastic materials, on photocurable resins,with simultaneous irradiation and photopolymerization.

With the aim of faithfully reproducing natural materials, a desiredfeature is to have the embossed structure in register with the printedimage, i.e. to obtain correspondence between concavity/convexity and theprinted image. With traditional processes, embossing in register is noteasy to obtain, both for the precision required and for the need formultiple molds corresponding to the various structures to be printedwith the corresponding image.

A method for reproducing the structure in a simple and efficient mannerwould be even more appropriate with digital printing, which allows toeasily produce different images.

In fact, modern scanners used to capture the image of materials, forexample METIS DRS 2000, also allow for the simultaneous capture of thesuperficial structure that may be advantageously used for embossing inregister.

Given the widespread use of embossing, it should have simplicity andcost-effectiveness features.

Currently, it is therefore desirable to find new methods for embossingitem surfaces, which are quick, easy, applicable in register on surfacesof different materials, as well as cost-effective.

SUMMARY OF THE INVENTION

According to an aspect of the invention, the Applicant has found out amethod for producing an embossing on a substrate by means of digitalprinting technology.

In particular, the method of the invention advantageously provides forthe application, by means of digital printing, of an embossing liquid ona portion of a coating or layer of a resin and/or ink and/or paintcontaining it preferably when the resin has not yet hardened or haspartially hardened. The deposition of the embossing liquid may produceconcavities or convexities on the resin layer/coating. The embossedresin is then polymerized, typically by means of UV curing, and theembossing liquid is removed. According to some embodiments, thepolymerization of the paint and the removal of the embossing liquid mayoccur simultaneously.

The Applicant has further unexpectedly found out that in the embossingmethod of the invention it is possible to use water as embossing liquid.

According to a first aspect, the invention therefore relates to a methodand an apparatus for generating a three dimensional surface comprisingthe steps of:

-   -   A) applying a paint on the surface of a material,    -   B) applying a water-based embossing liquid on the paint,    -   C) polymerizing the paint, preferably by means of UV or EB        (electron beam) irradiation,    -   D) removing the embossing liquid.

Embodiments of the present invention as defined above or as defined inclaim 1 are shown below.

The method of the invention reproduces a structure in register in anefficient and cost-effective manner.

Unlike the background art, which for Embossing in Registration (EIR)provides for the engraving of rollers or molds corresponding to theunderlying printed image, the method of the invention uses digitalprinting technology to produce the embossing of the substrate. Themethod of the invention is flexible and capable of managing individualfiles.

Furthermore, the embossed structure obtained by the method of theinvention has the desired features of resistance and hardness, since thecoating itself used for the protection of the substrate is embossed, asin the case of panels used in floorings or in furniture or in designfurnishings.

The versatility and the resolution obtainable by the method of theinvention allows for the use thereof also in applications wheremicrostructures typical of the field of microfluidics are used.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows two schematic reproductions of steps A)-C) of the processof the invention with the obtainment of a substrate with negativeembossing and positive embossing;

FIG. 2 shows an embodiment of an apparatus for reproducing the method ofthe invention;

FIG. 3 shows, by means of the laser profilometer analysis, a substratewith a decorative superficial embossing obtained by the method describedin Example 1.

DETAILED DESCRIPTION OF THE INVENTION

According to an aspect, the present invention relates to a method forproducing a three dimensional embossed coating on a substrate comprisingthe steps of:

A) applying a non-polymerized photocurable resin, or a paint or inkcontaining it, on the surface of a substrate thus forming a coating;

B) applying a water-based embossing liquid on at least one portion ofthe coating;

C) polymerizing the photocurable resin by means of irradiation with UVor EB beams (electron beam);

D) optionally removing the embossing liquid.

Within the scope of the invention, the inks and/or paints employed aresuitable for the coating of substrates to be decorated.

Typically, the coating layer resin may be of a various chemical naturesuch as, for example, a melamine, polyurethane, epoxy resin andpreferably a photocurable resin.

Preferably, the resin has a high solid content, for example equal to20-30% by weight with respect to the weight of the resin, so as tomaximize the embossable layer and vanish the effect of the embossingliquid due to the evaporation of the solvent, if any.

Preferably, the resins used are photocurable.

For example, photocurable resins may be divided in two types, on thebasis of the curing mechanism: 1) radical, typically acrylate resins andvinyl monomers 2) cationic resins, such as epoxy, polyols and monomerssuch as oxetans and vinyl ethers.

Type 1 may be divided in different subcategories: epoxy acrylates,urethane acrylates, polyester acrylates, polyether acrylates, aminoacrylates, silicone acrylates, polyisoprene acrylates, polybutadieneacrylates and acrylate monomers. The term acrylates means both acrylateand methacrylate resins.

Vinyl monomers include N-vinyl caprolactam (NVC), acryloyl morpholine(ACMO), diethylene glycol divinyl ether (DVE-2), triethylene glycoldivinyl ether (DVE-3) and mixtures thereof.

The previously described resins are associated in that they polymerizeand harden by virtue of the energy irradiated by ultraviolet beamdevices.

In a preferred embodiment of the invention, the coating layer paintcomprises one or more photocurable resins, photoinitiators, fillers,such as, for example, aluminum oxide, to increase the abrasionresistance thereof, talc to modify the rheology thereof, silica toreduce the brilliance thereof, calcium carbonate and other additives,for example, leveling agents, wetting agents, slip agents, rheologymodifiers, commonly used to protect floor and furniture surfaces fromwear, scratches and abrasions.

Advantageously, the photocurable resin contains silicones which arecapable of increasing the depth of the embossing. Typically, siliconesare added from 0.01% to 20%, from 0.01% to 10%, from 0.01% to 2%. Thevarious usable products include silicones, silicone polyethers, siliconeacrylates, silicone polyether acrylates.

With the same effect, the formulation of the photocurable resin maycontain rheology modifiers, such as thixotropic agents, which have thefunction of maintaining the embossing shape better, both in terms ofdepth and of definition.

Typically, the resin used is a photocurable resin and the photocuring isobtained by means of conventional technology, as described, for example,in the book “Radiation Curing: Science and Technology” (Pappas).

In an preferred embodiment of the invention, the coating layer is aphotocurable printing paint and/or a photocurable printing ink appliedby means of digital printing.

The substrate usable in the method of the invention may be a material ofa different nature, such as wood and derived products, for example MDF,HDF, particleboard, multilayer wood, cellulose-based materials, such aspaper or cardboard, metals, plastic material, stone, glass, ceramic andcomposite thereof.

The substrate is selected depending on the application of the method ofthe invention, for example for the coating of furniture, floors,fixtures, profiles.

In an embodiment, the embossing liquid is water-based. This liquid hasthe advantage of having a high surface tension, of being easilyremovable and of being cost-effective.

In some embodiments, the water-based embossing liquid contains additiveswhich serve to modify properties thereof, such as surface tension and/orrheology and/or printability and/or color.

In particular, the addition of surface tension modifiers helpsstabilizing the liquid and improves the printability, especially whenusing inkjet printers.

In some embodiments, the embossing liquid comprises silicones orsilicone acrylates. The presence of silicones improves the embossabilityand provides a natural appearance to the treated coating, which may beparticularly appreciated from an aesthetic point of view.

The various usable products include silicones, silicone polyethers,silicone acrylates, silicone polyether acrylates.

According to some embodiments, the embossing liquid may contain furthersubstances adapted to improve the embossing effect and/or impartdifferent functionalities beyond the embossing and may comprisephotoinitiators, leveling agents, oils, light stabilizers, antioxidants,biocides, pigments, rheology modifiers, humectants, antifoams andmixtures thereof.

The control of the embossing depth or the embossed layer thickness maybe modulated in different manners, either by applying more embossingliquid, or by increasing or decreasing time between the application ofthe embossing liquid and the subsequent polymerization of the paint.Thereby, by acting more or less the embossing liquid, more or less deepembossings may be obtained, which are both negative (concavities) andpositive (convexities).

Preferably, to create a neat and precise effect, the embossing liquidhas a surface tension higher than the paint to be embossed, while inother cases the surface tension may be lowered to obtain a more gentleembossment.

The substrate layer/coating has a variable thickness.

By way of example, the coating may have a thickness in the range from 1to 400μ, from 2 to 100μ, from 3 to 50μ in the portion withoutembossings, and a thickness in the range of 0.05 to 100μ, 0.5 to 50μ, 1to 25μ in the embossed areas.

The process of the invention and the apparatus for the achievementthereof will become more apparent from the following description, inwhich reference is made to the embodiments shown in the accompanyingFIGS. 1 and 2.

According to some embodiments, the resin or paint or ink containing itto be embossed may be applied on the substrate by means of digitaltechnology, for example, as shown in FIG. 2, point 2, using inkjetprinting or by means of conventional techniques in use, such asroller/spray/thin layer/die/slot-die.

In some embodiments of the invention, the application of the embossingliquid takes place on the resin or paint or ink that contain it, nothardened, of an underlying printed image.

Typically, photopolymerization by UV irradiation may be performed bymeans of one or more Hg lamps and/or LED lamps, as shown, for example,in FIG. 2, point 5. Preferably, the lamps are mounted on a mobilesystem, which allows to bring them more or less closer to the embossingliquid application system, so as to better control the action thereofand thereby modulate the effect thereof. For example, to obtain a dullmatt effect, the pre-polymerization/polymerization shall take placeimmediately after the inkjet application, as shown in FIG. 2, point 4.

The removal of the embossing liquid may take place simultaneously to thephotopolymerization as shown in FIG. 2, point 5, as the UV lamp emitsheat, or may take place at a distinct step. In such case, the removal ofthe embossing liquid (step D) may be performed by means of the usualtechnologies adapted to make the water evaporate, such as, for example,infrared beams or hot air irradiation.

In another embodiment of the invention, the application of the embossingliquid is performed in two distinct steps, and this allows, for example,to obtain combined effects by using two embossing liquids.

Typically, the method of the invention provides for the application ofthe embossing liquid by means of an inkjet printhead.

Inkjet printing may be either in multipass/scanning mode, where theimage is generated with multiple passages of the printhead while thematerial to be printed advances, or in singlepass mode, where thematerial to be printed passes only once under the printheads which areinstalled along the maximum width of the material itself. Singlepassprinting is used for large runs, while multipass printing is definitelythe most common one.

Typically, inkjet printing provides for the use of a printhead to createand lay the liquid droplets that will then form the image to be printed.By way of example, details of this type of printing may be found in thebook “Fundamentals of inkjet printing: the science of inkjet anddroplets” (Hoath, Stephen).

Depending on the inkjet printhead used, the droplets produced may havedifferent volumes and consequently different diameters. By way ofexample, the following table shows the volume of the drop and thecorresponding diameter.

TABLE 1 VOLUME VOLUME VOLUME VOLUME DIAMETER Lev. 1 Lev. 2 Lev. 3 (pl)(μ) (pl) (pl) (pl) 1.5 3 1.5 3 4.5 2.4 5 2.4 4.8 7.2 3 6 3 6 9 6 13 6 1218 10 21 10 20 30 12 25 12 24 36 30 64 30 60 90 80 170 80 160 240

In addition to the native size of the drop, which is an intrinsicfeature of the printhead, larger drops may be generated by the printheaditself. For example, a printhead capable of laying 4 levels of gray willhave the smallest drop measuring 6 pl while the largest will measure 18pl (Table 1).

Advantageously, the application of small drops may be used to generatemicrogrooves and microwells measuring a few microns, typical ofmicrofluidics, for the production of sensors and functional devices.

A further application of the small drops allows for the generation ofmicrostructures, which make the surface of the embossed paint/resin/inkmatt. With this latter application, glossy and matt surfaces may beobtained simultaneously, with interesting aesthetic effects.

In another embodiment of the invention, the resin to be embossed maycontain expanding agents so as to obtain high embossing volumes, whilelimiting the weight of the embossed layer and/or the cost. Typically,hollow polymeric microspheres filled with gas may be used, which, atcertain temperatures, increase in volume; for example EXPANCELs may beused. The expansion step preferably takes place prior to the applicationof the embossing liquid.

In addition to reproducing natural materials such as wood and stones,the method of the invention may also be used to generate threedimensional structures, typical of the graphic and/or decorative field.

Advantageously, the method of the invention may be used to embossprinted surfaces in a traditional manner (rotogravure/flexo/offset).

The following embodiments are provided purely for the purpose ofillustrating the present invention and are not intended to limit thescope of protection defined by the appended claims.

Example 1

50 g/sqm of photocurable paint (Renner UO-240) for finishing floors wereapplied in line at 15 m/min to a MDF panel, by means of a paint roller.Subsequently, the panel was passed under an inkjet printer of thesinglepass type, with which the embossing liquid consisting of H₂O+2% ofTEGO RAD 2100 (acrylate silicone) was applied. After the application,the convexities produced by the embossing liquid on the paint becomeapparent. The printer used (CEFLA) was equipped with DIMATIX STARFIRE1024 printheads, while the printed image was obtained from a threedimensional scan, performed with a scanner (METIS), of a natural oaksection. The image was then uploaded to the printer by means of thededicated software (RIP). Subsequently, the panel was irradiated with160 w/cm ultraviolet light generated by a medium-pressure Hg lamp. Inaddition to the UV beams, the lamp generates heat, which in this case issufficient to make the water contained in the embossing liquid evaporatewhile the acrylate silicone contained in the embossing liquid ispolymerized by means of the UV lamp. Following the photopolymerization,the resin is dry and hard to the touch, with the printed woodgrainimpressed, the embossing is well defined and detailed exactly like thescanned natural material. The structure is best seen by means of thelaser profilometer analysis (3D profiler—USA), as shown in FIG. 3.

Example 2

A photocurable gray varnish (100 g/sqm) was applied to a supportmaterial. Subsequently, the support was passed under an inkjet printerof the singlepass type equipped with DIMATIX STARFIRE 1024S printheads,with which the embossing liquid consisting of H₂O was applied. Thesupport was then irradiated with 160 w/cm ultraviolet light generated bya medium-pressure Hg lamp. On the surface, the printed image consistingof a text with variable fonts is well apparent.

Example 3

A high gloss photocurable paint (Renner UO-240) was applied to a supportmaterial.

The support was passed under an inkjet printer of the singlepass typeequipped with DIMATIX STARFIRE 1024S printheads, the smallest drop ofwhich is 10 pl, with which the embossing liquid consisting of H₂O wasapplied using only the smallest drops. The support was then immediatelyirradiated with a 395 nm 8 w/cm² PHOSEON FIRELINE lamp and subsequentlywith a 160 w/cm medium-pressure DR. Hönle Hg lamp to complete thepolymerization of the paint. The paint is homogeneously matt due to themicrostructure generated by the microdrops laid by the inkjet printhead.The original paint was in fact equal to 85 gloss units, while, followingthe application, the paint was equal to 35 gloss units.

Example 4

20μ of a photocurable formulation were applied to a support material(PET).

The support was passed under an inkjet printer of the multipass type,with which the embossing liquid consisting of H₂O+2% of PEG600DA(acrylate monomer) was applied only using the smallest drops. Theprinthead used was a DIMATIX STARFIRE 1024S, the smallest drop of whichmeasures 10 pl. The support was immediately irradiated with ultravioletlight generated by a 8 w/cm² PHOSEON FIRELINE lamp). Subsequently, aphotocurable formulation was completely polymerized by means ofirradiation with ultraviolet light generated by a 160 w/cmmedium-pressure DR. Hönle Hg lamp. The surface appears hard, withmicrogrooves and microwells measuring variably from 12 to 25 microns,which can be clearly identified using a Dino Lite 4113 microscope.

The invention claimed is:
 1. A method for producing a three dimensionalsurface on a substrate comprising the steps of: A) applying aphotocurable resin, or a paint or ink containing the photocurable resin,on a surface of a substrate, thus forming a coating; B) applying awater-based embossing liquid on a portion of the coating; C)polymerizing the photocurable resin by irradiation with UV beams; and D)removing the embossing liquid.
 2. The method according to claim 1,wherein the photocurable resin is configured to be polymerized in aradical and/or cationic way.
 3. The method according to claim 2 whereinthe photocurable resin is selected from the group consisting of acrylateresins, acrylate monomers, vinyl monomers and mixtures thereof, epoxyresins, polyols, oxetanic monomers, vinyl monomers, and mixturesthereof.
 4. The method according to claim 2, wherein the photocurableresin is selected from the group consisting of epoxy acrylates, urethaneacrylates, polyester acrylates, polyether acrylates, amino acrylates,silicone acrylates, polyisoprene acrylates, polybutadiene acrylates,acrylate monomers and mixtures thereof, and vinyl resins are selectedfrom the group consisting of N-vinyl caprolactam (NVC), acryloylmorpholine (ACMO), diethylene glycol divinyl ether (DVE-2), andtriethylene glycol divinyl ether (DVE-3) and mixtures thereof.
 5. Themethod according to claim 1, wherein the photocurable resin comprisesone or more expanding agents, which are expanded prior to the applyingof the embossing liquid.
 6. The method according to claim 1, wherein theembossing liquid is water-based or consists of water.
 7. The methodaccording to claim 6 wherein the embossing liquid contains at least onesubstance selected from the group consisting of surface tensionmodifiers, acrylic resins, photocurable resins, photoinitiators, slipagents, wetting agents, oils, light stabilizers, antioxidants,antifoams, humectants, biocides, colorants, fillers, and pigments andmixtures thereof.
 8. The method according to claim 1, wherein theembossing liquid comprises silicones and/or silicone acrylates.
 9. Themethod according to claim 1, wherein the embossing liquid has a highersurface tension than a paint to be embossed.
 10. The method according toclaim 1, wherein said photocurable resin is contained in a coloredand/or pigmented paint.
 11. The method according to claim 1, wherein theembossing liquid is applied with an inkjet printhead.
 12. The methodaccording to claim 1, wherein the embossing liquid is applied in two ormore distinct steps using different inkjet printing systems.
 13. Themethod according to claim 1, wherein the method comprises embossingperformed in line with a printing and finishing of a material.
 14. Themethod according to claim 1, wherein the method comprises embossingapplied in register with a printed image.
 15. The method according toclaim 1, wherein the steps of polymerizing the photocurable resin or ofthe paint containing the photocurable resin and of removing of theembossing liquid takes place simultaneously.
 16. The method according toclaim 1, wherein the step of polymerizing the photocurable resin or ofthe paint containing the photocurable resin takes place in severaldistinct steps, comprising a first pre-polymerization/gelation step and,subsequently, a polymerization step.
 17. The method according to claim1, further comprising the step of generating a matt surface.
 18. Themethod according to claim 1, further comprising the step of generatingglossy and matt areas simultaneously on a surface of the paint.
 19. Themethod according to claim 1, further comprising the step of generatingan embossed surface, and wherein, after removal of the embossing liquid,a cover paint is applied on the embossed surface so as to providefurther protection and/or to matt the embossed surface.
 20. Thesubstrate or article obtained by the method according to claim 1,wherein the substrate is adapted to produce or coat floors, furniture,design and architectural surfaces, commercial and/or packaging printing,or is adapted to produce sensors and functional for use inmicrofluidics. 21.-22. (canceled)
 23. An apparatus for producing a threedimensional surface on a substrate according to claim 1, comprising: oneor more inkjet printing systems, a mobile photopolymerization systempositionable near an application area of an embossing liquid, andoptionally, an embossing liquid evaporation system and/or aphotopolymerization system.